[commit: ghc] master: Testsuite: add regression test for missing class constraint (029367e)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/029367e5894d4ac3ea3845f39f2cc1b5a6a9fac1/ghc

>---------------------------------------------------------------

commit 029367e5894d4ac3ea3845f39f2cc1b5a6a9fac1
Author: Thomas Miedema <thomasmiedema at gmail.com>
Date:   Mon Jul 20 15:40:59 2015 +0200

    Testsuite: add regression test for missing class constraint
    
    The following program is accepted by ghc-7.0 to ghc-7.10, but rejected
    by ghc-6.12.3 and HEAD (and rightfully so):
    
        class Class1 a
        class Class1 a => Class2 a
        class Class2 a => Class3 a
        instance Class3 a => Class2 a
    
    The last line is missing a `Class1 a` constraint. Add a regression test
    for this (typechecker/should_fail/tcfail223).
    
    Add similar missing class constraints to T7126 and T5751. I verified
    that the these changes don't interfer with the intention of the tests
    (they still result in a loop with ghc-7.4.1).
    
    Reviewers: austin, simonpj, bgamari
    
    Reviewed By: bgamari
    
    Subscribers: rwbarton, thomie
    
    Differential Revision: https://phabricator.haskell.org/D1078


>---------------------------------------------------------------

029367e5894d4ac3ea3845f39f2cc1b5a6a9fac1
 testsuite/tests/typecheck/should_fail/all.T            |  1 +
 testsuite/tests/typecheck/should_fail/tcfail223.hs     | 10 ++++++++++
 testsuite/tests/typecheck/should_fail/tcfail223.stderr |  9 +++++++++
 testsuite/tests/typecheck/should_run/T5751.hs          |  2 +-
 testsuite/tests/typecheck/should_run/T7126.hs          |  2 +-
 5 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/testsuite/tests/typecheck/should_fail/all.T b/testsuite/tests/typecheck/should_fail/all.T
index d1bf03b..fbbeddb 100644
--- a/testsuite/tests/typecheck/should_fail/all.T
+++ b/testsuite/tests/typecheck/should_fail/all.T
@@ -246,6 +246,7 @@ test('tcfail219', normal, multimod_compile_fail, ['tcfail219.hsig', '-sig-of "Sh
 test('tcfail220', normal, multimod_compile_fail, ['tcfail220.hsig', '-sig-of "ShouldFail is base:Prelude"'])
 test('tcfail221', normal, multimod_compile_fail, ['tcfail221.hsig', '-sig-of "ShouldFail is base:Prelude"'])
 test('tcfail222', normal, multimod_compile_fail, ['tcfail222.hsig', '-sig-of "ShouldFail is base:Data.STRef"'])
+test('tcfail223', normal, compile_fail, [''])
 
 test('SilentParametersOverlapping', normal, compile, [''])
 test('FailDueToGivenOverlapping', normal, compile_fail, [''])
diff --git a/testsuite/tests/typecheck/should_fail/tcfail223.hs b/testsuite/tests/typecheck/should_fail/tcfail223.hs
new file mode 100644
index 0000000..e5e0d5c
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/tcfail223.hs
@@ -0,0 +1,10 @@
+{-# LANGUAGE FlexibleInstances, UndecidableInstances #-}
+module ShouldFail where
+
+class Class1 a
+class Class1 a => Class2 a
+class Class2 a => Class3 a
+
+-- This was wrongfully accepted by ghc-7.0 to ghc-7.10.
+-- It is missing a `Class1 a` constraint.
+instance Class3 a => Class2 a
diff --git a/testsuite/tests/typecheck/should_fail/tcfail223.stderr b/testsuite/tests/typecheck/should_fail/tcfail223.stderr
new file mode 100644
index 0000000..e4a4fcd
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/tcfail223.stderr
@@ -0,0 +1,9 @@
+
+tcfail223.hs:10:10: error:
+    Could not deduce (Class1 a)
+      arising from the superclasses of an instance declaration
+    from the context: Class3 a
+      bound by the instance declaration at tcfail223.hs:10:10-29
+    Possible fix:
+      add (Class1 a) to the context of the instance declaration
+    In the instance declaration for ‘Class2 a’
diff --git a/testsuite/tests/typecheck/should_run/T5751.hs b/testsuite/tests/typecheck/should_run/T5751.hs
index 423a407..7c7d8ab 100644
--- a/testsuite/tests/typecheck/should_run/T5751.hs
+++ b/testsuite/tests/typecheck/should_run/T5751.hs
@@ -25,7 +25,7 @@ main =
 class (Widgets x) => MonadRender x
 class (XMLGenerator m)  => Widgets m
 -- instance Widgets (IdentityT IO) -- if you uncomment this, it will work
-instance MonadRender m => Widgets m
+instance (XMLGenerator m, MonadRender m) => Widgets m
 instance MonadRender (IdentityT IO)
 
 web :: ( MonadIO m
diff --git a/testsuite/tests/typecheck/should_run/T7126.hs b/testsuite/tests/typecheck/should_run/T7126.hs
index ce9792d..184d5df 100644
--- a/testsuite/tests/typecheck/should_run/T7126.hs
+++ b/testsuite/tests/typecheck/should_run/T7126.hs
@@ -24,7 +24,7 @@ class Class2 a => Class3 a where
 instance Class1 Int where
   func1 = id
 
-instance Class3 a => Class2 a where
+instance (Class1 a, Class3 a) => Class2 a where
   func2 = func3
 
 instance Class3 Int where